Fuel cell systems enable electrical power to be generated with low emissions and a high level of efficiency. For this reason, at present efforts are also being made in aeroplane construction to use fuel cell systems to generate the electrical energy required on board an aeroplane. For example, it is conceivable to partially replace the generators that are currently utilized to supply on-board power, which are driven by the main engines or the auxiliary turbine, by a fuel cell system. Moreover, a fuel cell system could also be utilized for the emergency supply of power to the aeroplane and replace the ram air turbine (RAT) which has been utilized hitherto as an emergency power unit.
Fuel cells conventionally include a cathode region and an anode region, separated from the cathode region by an electrolyte. When the fuel cell is operated, a fuel, for example hydrogen, is supplied to the anode side of the fuel cell and an oxygen-containing oxidant, for example air, is supply to the cathode side of the fuel cell. In the case of a polymer electrolyte membrane fuel cell, the hydrogen molecules react, at an anode catalyst in the anode region, for example in accordance with the equationH2→2.H++2.e−and in so doing form positively charged hydrogen ions and give off electrons to the electrode.
The H+ ions which are formed in the anode region then diffuse through the electrolyte to the cathode, where they react, at a cathode catalyst in the cathode region, with the oxygen supplied to the cathode and the electrons that are fed to the cathode by way of an external circuit, in accordance with the equation0.5.O2+2.H++2.e−→H2Oto form water.
To minimise pressure losses inside the fuel cell system, to ensure that the distribution of gas to the electrodes of the fuel cell is uniform and to keep the volume of flow through the fuel cell as small as possible, it is advantageous to supply the cathode of a fuel cell with compressed air, that is air which is at a pressure above atmospheric pressure.
An object of the invention is to provide an aircraft fuel cell system which makes it possible to supply a fuel cell with compressed air in an energy-efficient manner. Further, an object of the invention is to provide a method of operating an aircraft fuel cell system of this kind.